So after building the IF Filter haphazard looking like a spastic, I connected up the test gear to run a Bode Plot to see the shape of the filter. I then proceeded to sit here wondering what i did wrong for the next hour as my 500hz CW Filter is almost 4K wide and probably ok as an AM Filter. LOL. Well, slow as slow can be it dawned on me, I grabbed 470 capacitors out of the box, thinking they were 470pf not 471 capacitors which are 470 pf. So in my haste and not thinking i have 47pf capacitors in my filter not what i originally planned.
On a positive note, the shape is not all that bad and not to much ripple even though the input to the filter is not correctly terminated. That is another headache, trying to get accurate measurements of in and output impedances and matching right when you have not built the preceeding stages. So I am going to switch to Termination Insensitive Amps for the IF and make my life easier.
So i had another swing at the MPSH10 in LT Spice and what it says should happen and what actually is happening are 2 very different things. I got it sorted and it is working fine. But I am not sure if i run with this or revert back to the 2n3904. For now I will run with this and see how it goes, I just have to measure the input and output impedances. Which as of next week or so, will be easier when i have a vna. The circuit is a little different to what was in the schematic in the previous post. I will update the schematic if I end up running with these.
I build this a little different, I had these squares sitting there i made so I used them.
Oscilloscope output, green trace is the signal in, yellow signal out.
Output from the spectrum analyzer.
So i got busy today and wired up the uBitx. Turned it on and tuned around a little to find some signals, well there was not much going on anywhere but I did manage to find this one ZL on an other wise dead band. Its good to know that the receiver works, now i just have to wire up a mic and check its working on transmit. But that is going to be another day.
So I recorded a little video from tonight’s 7.130 dx net. I have been giving the receiver a good workout to see how I like it. So far, to be honest, I think i prefer the Bitx40 over the uBitx. Though, it might be I just need to play with the IF and BFO settings to move the bandpass around a little to where I think it sounds better.
While QRP Labs makes some wonderful kits, they really could do with adding 20% more board area so that old sausage fingers can got in there and do some Da Finger Poken. I get that some things really need to be packed in tight, but others do not and I think the filter boards can be much bigger and contain a 2nd set of holes for the wires rather than trying to solder them to the tops of the header pins. Anyway that’s enough moaning from me. The kit is going together well all tests have been successful and I am confident that it will eventually power on and work.
I got reading glasses a few months back, but I can tell you I am really noticing how hard some things are to do, to solder that one smd park i had to use both my glasses and the huge magnifying glass to get the job done 🙂
I love it when a plan comes together, needed 3.1uh on the 2 inductors, and guess what I got, 3.1uh HAHAHA.
I still have the polyphase board to build. Then i need to start working out what bits i am going to add to it to make it complete. Arduino and SI5351A obviously and some kind of AF amp should do the trick. More on this to come.